Why do cats knock things over?

[Catherine]

All of those things are true and probably more. Cats like to do stuff. They love watching things fall. 
We like to put things on window ledges. Cats like to push things off of window ledges.
Maybe we need a set of cat toys that look like ornaments. 
We can place them on window ledges, counters, tables, anything a cat can push them off of. Think of the fun the cat would have. If they were unbreakable we could just put them back before we go out each day. It would keep the cat busy for a while and protect stuff we don't want on the floor. 
They could sell the toys in a bag labeled "Things for your Cat to push off the Table". 

We may never know all the reasons cats push things over, but we can learn to live with it.